The endocrine pancreas is both the substrate for fundamental questions in developmental biology as well as the target of the disease diabetes mellitus, which affects millions of individuals worldwide. A detailed genetic and molecular understanding of pancreatic endocrine development will be essential if we are to manipulate islet cell fate and numbers in vivo. Our emerging understanding of pancreatic development is one in which, through interactions with surrounding mesenchyme, the initially unpatterned pancreatic epithelium is successively sub-divided into exocrine and endocrine compartments which subsequently differentiate, the latter containing the |3eta cells that produce insulin. Among the factors that dictate islet cell specification are many genes whose identities are now known. In fact, it is now possible to order these genes into a first order genetic regulatory network in terms of order of gene action, expression and functional interdependencies, and hierarchical relationships. This grant therefore poses the question: Do we already know enough, and can we sufficiently augment that knowledge, to begin to use this information to systematically engineer islets and islet cells in vitro? To accomplish this ambitious goal, we will undertake three Specific Aims that are highly integrated with multiple components of SysCODE. In Aim 1, we will generate complete gene lists for key early states in the developing endocrine pancreas. An initial effort in this area has already been accomplished (Gu et al., Development 131, 165-79, 2004). We will now augment this information with data from additional developmental stages, selected mutant states and first-generation proteomic analyses. In Aim 2, in conjunction with the SysCODE Computational Team, we will develop methodology to order these genes and selected proteins into a definitive gene regulatory network (CRN) in a format that is useful to both biologists and tissue engineers. Lastly, in Aim 3 we will collaborate with the SysCODE Tissue Engineering Team to implement a stem cell based, engineered model of pancreatic islet development and we will use the GRNs generated in Aim 2 to optimize pancreatic endocrine fate specification. In the out years of the grant, we will transplant the engineered islets into diabetic mice and assess their physiological function. Collectively, these efforts, in conjunction with the rest of SysCODE, will establish a transforming paradigm for regenerative medicine.